Synergistic interaction of p185c-neu and the EGF receptor leads to transformation of rodent fibroblasts

Activation of Neu (ErbB-2) mediated by disulfide bond-induced dimerization reveals a receptor tyrosine kinase dimer interface

Receptor dimerization is a crucial intermediate step in activation of signaling by receptor tyrosine kinases (RTKs). However, dimerization of the RTK Neu (also designated ErbB-2, HER-2, and p185(neu)), while necessary, is not sufficient for signaling. Earlier work in our laboratory had shown that introduction of an ectopic cysteine into the Neu juxtamembrane domain induces Neu dimerization but not signaling. Since Neu signaling does require dimerization, we hypothesized that there are additional constraints that govern signaling ability. With the importance of the interreceptor cross-phosphorylation reaction, a likely constraint was the relative geometry of receptors within the dimer. We have tested this possibility by constructing a consecutive series of cysteine substitutions in the Neu juxtamembrane domain in order to force dimerization along a series of interreceptor faces. Within the group that dimerized constitutively, a subset had transforming activity. The substitutions in this subset all mapped to the same face of a predicted alpha helix, the most likely conformation for the intramembrane domain. Furthermore, this face of interaction aligns with the projected Neu* V664E substitution and with a predicted amphipathic interface in the Neu juxtamembrane domain. We propose that these results identify an RTK dimer interface and that dimerization of this RTK induces an extended contact between juxtamembrane and intramembrane alpha helices.

Differential endocytic routing of homo- and hetero-dimeric ErbB tyrosine kinases confers signaling superiority to receptor heterodimers

Both homo- and hetero-dimers of ErbB receptor tyrosine kinases mediate signaling by a large group of epidermal growth factor (EGF)-like ligands. However, some ligands are more potent than others, although they bind to the same direct receptor. In addition, signaling by receptor heterodimers is superior to homodimers. We addressed the mechanism underlying these two features of signal tuning by using three ligands: EGF; transforming growth factor alpha (TGFalpha); and their chimera, denoted E4T, which act on cells singly expressing ErbB-1 as a weak, a strong, and a very strong agonist, respectively. Co-expression of ErbB-2, a developmentally important co-receptor whose expression is frequently elevated in human cancers, specifically potentiated EGF signaling to the level achieved by TGFalpha, an effect that was partially mimicked by ErbB-3. Analysis of the mechanism underlying this trans-potentiation implied that EGF-driven homodimers of ErbB-1 are destined for intracellular degradation, whereas the corresponding heterodimers with ErbB-2 or with ErbB-3, dissociate in the early endosome. As a consequence, in the presence of either co-receptor, ErbB-1 is recycled to the cell surface and its signaling is enhanced. This latter route is followed by TGFalpha-driven homodimers of ErbB-1, and also by E4T-bound receptors, whose signaling is further enhanced by repeated cycles of binding and dissociation from the receptors. We conclude that alternative endocytic routes of homo- and hetero-dimeric receptor complexes may contribute to tuning and diversification of signal transduction. In addition, the ability of ErbB-2 to shunt ligand-activated receptors to recycling may explain, in part, its oncogenic potential.

ErbB2 expression increases the spectrum and potency of ligand-mediated signal transduction through ErbB4

Interleukin 3-dependent murine 32D cells do not detectably express members of the ErbB receptor family and do not proliferate in response to known ligands for these receptors. 32D transfectants were generated expressing human ErbB4 alone (32D.E4) or with ErbB2 (32D.E2/E4). Epidermal growth factor (EGF), neuregulin 1-beta (NRG1-beta), betacellulin (BTC), transforming growth factor-alpha (TGF-alpha), heparin binding-EGF (HB-EGF), and amphiregulin were analyzed for their ability to mediate mitogenesis in these transfectants. 32D.E4 responded mitogenically to NRG1-beta and BTC. Surprisingly, EGF also induced significant DNA synthesis and TGF-alpha was negligibly mitogenic on 32D.E4 cells, whereas HB-EGF and amphiregulin were inactive. Although coexpression of ErbB2 with ErbB4 in 32D.E2/E4 cells did not significantly alter DNA synthesis in response to NRG1-beta or BTC, it greatly enhanced mitogenesis elicited by EGF and TGF-alpha and unmasked the ability of HB-EGF to induce proliferation. EGF-related ligands that exhibited potent mitogenic activity on 32D.E2/E4 cells at low concentrations induced adherence, morphological alterations, and up-regulation of the Mac-1 integrin and FcgammaRII/III at higher concentrations. While 125I-EGF could be specifically crosslinked to both 32D.E4 and 32D.E2/E4 cells, its crosslinking capacity was greatly enhanced in the cotransfected cells. The ability of the various ligands to mediate proliferation and/or adhesion in the two transfectants correlated with their capacity to induce substrate tyrosine phosphorylation and to initiate and sustain activation of mitogen-activated protein kinase. We conclude that the ability of ErbB4 to mediate signal transduction through EGF-like ligands is broader than previously assumed and can be profoundly altered by the concomitant expression of ErbB2.

The role of transforming growth factor alpha production and ErbB-2 overexpression in induction of tumorigenicity of lung epithelial cells

Over-expression of erbB-2 is associated with shortened survival of patients with lung adenocarcinomas. We demonstrated that human lung epithelial cells, overexpressing erbB-2, formed tumours in nude mice only when high levels of transforming growth factor (TGF)-alpha were produced (E6T cells). To define the role that TGF-alpha production played in induction of tumorigenicity, a non-tumorigenic TGF-alpha-negative clone of ErbB-2 overexpressing cells (E2 cells) was transfected with an expression vector for TGF-alpha (E2alpha cells). Transfected clones produced TGF-alpha at 11-25% of the level produced by the E6T cell line. Tumorigenic E6T cells transfected with a TGF-alpha antisense vector (E6TA cells) expressed only 6% of the TGF-alpha level of the parental cells. Clones of E6T, E6TA, E2 and E2alpha were inoculated into athymic nude mice to measure tumorigenic potential. E6T cells formed tumours with a 70% efficiency. E2, E6TA and E2alpha cells failed to form tumours. The levels of EGFR were similar in non-tumorigenic E2 and tumorigenic E6T cells but higher in E2alpha and E6TA cells, and ErbB-2 were greatly overexpressed in an E2alpha clone. In vitro, ErbB-2 co-immunoprecipitated with EGFR in lysates of unstimulated E6T and E2alpha TGF-alpha-producing cells, indicating that the lower TGF-alpha levels were sufficient to induce in vitro heterodimerization. These studies suggest that induction of the tumorigenic phenotype depends on achieving a threshold level of TGF-alpha sufficient to activate downstream signalling by ErbB-2 containing active heterodimers.

Immunologic approaches to inhibiting cell-surface-residing oncoproteins in human tumors

The erbB family of receptor tyrosine kinases are growth factor receptors that are overexpressed or mutated in a large variety of human cancers. Studies of erbB-mediated signal transduction will lead to an understanding of the role played by this family of receptors in normal and transformed cells. In this article, we discuss the contemporary understanding of the structure and function of these receptors, and how these features might be exploited in immunologic strategies of receptor-based growth inhibition. The first part of this article details the structure of erbB receptors as it relates to the process of transformation of cells and the malignant phenotype in human tumors. In the second part of this article, we discuss immunologic approaches to therapy for cancers in which surface-residing erbB receptors are overexpressed or mutated, with an emphasis on studies targeting the p185neu/c-erbB2 oncoprotein. The potential for antireceptor immunity and the evolution of small molecules for receptor-based immunotherapy are discussed. These studies provide a basis for the application of receptor-based strategies of growth inhibition in erbB-expressing human cancers.

The ErbB-2/HER2 oncogenic receptor of adenocarcinomas: from orphanhood to multiple stromal ligands

Extensive clinical and biochemical evidence implicates ErbB-2, a transmembrane tyrosine kinase related to growth factor receptors, in the development, metastasis, and resistance to therapy of multiple, common human carcinomas. Previous attempts to uncover an ErbB-2-specific ligand led to isolation of the neuregulin (NRG) family, but these ligands, like all other growth factors with an EGF-like motif, only indirectly active ErbB-2. On the other hand, biochemical and genetic evidence suggest a non-autonomous function of ErbB-2 in an interactive ErbB signaling network. Accordingly, the oncoprotein acts as a shared signaling subunit of primary growth factor receptors. By stabilizing heterodimers with other ErbB proteins, ErbB-2 prolongs and enhances signal transduction by a large group of stroma-derived growth factors. Furthermore, we have proposed a model in which all ErbB-2 ligands are bivalent and bind to ErbB-2 with low affinity, following high affinity binding to a primary receptor with which ErbB-2 is heterodimerized. Thus the presence of ErbB-2 in relevant ErbB heterodimeric structures on the surfaces of certain epithelial tumor cells can amplify signals arising from the binding of stromal ErbB ligands. This effect, in turn, may promote the growth of carcinoma cells.

Specificity within the EGF family/ErbB receptor family signaling network

Recent years have witnessed tremendous growth in the epidermal growth factor (EGF) family of peptide growth factors and the ErbB family of tyrosine kinases, the receptors for these factors. Accompanying this growth has been an increased appreciation for the roles these molecules play in tumorigenesis and in regulating cell proliferation and differentiation during development. Consequently, a significant question has been how diverse biological responses are specified by these hormones and receptors. Here we discuss several characteristics of hormone-receptor interactions and receptor coupling that contribute to specificity: 1) a single EGF family hormone can bind multiple receptors; 2) a single ErbB family receptor can bind multiple hormones; 3) there are three distinct functional groups of EGF family hormones; 4) EGF family hormones can activate receptors in trans, and this heterodimerization diversifies biological responses; 5) ErbB3 requires a receptor partner for signaling; and 6) ErbB family receptors differentially couple to signaling pathways and biological responses.

Epidermal growth factor and betacellulin mediate signal transduction through co-expressed ErbB2 and ErbB3 receptors

Interleukin-3 (IL-3)-dependent murine 32D cells do not detectably express epidermal growth factor receptors (EGFRs) and do not proliferate in response to EGF, heregulin (HRG) or other known EGF-like ligands. Here, we report that EGF specifically binds to and can be crosslinked to 32D transfectants co-expressing ErbB2 and ErbB3 (32D.E2/E3), but not to transfectants expressing either ErbB2 or ErbB3 individually. [125I]EGF-crosslinked species detected in 32D. E2/E3 cells were displaced by HRG and betacellulin (BTC) but not by other EGF-like ligands that were analyzed. EGF, BTC and HRG also induced receptor tyrosine phosphorylation, activation of downstream signaling molecules and proliferation of 32D.E2/E3 cells. 32D transfectants were also generated which expressed an ErbB3-EGFR chimera alone (32D.E3-E1) or in combination with ErbB2 (32D. E2/E3-E1). While HRG stimulation of 32D.E3-E1 cells resulted in DNA synthesis and receptor phosphorylation, EGF and BTC were inactive. However, EGF and BTC were as effective as HRG in mediating signaling when ErbB2 was co-expressed with the chimera in the 32D.E2/E3-E1 transfectant. These results provide evidence that ErbB2/ErbB3 binding sites for EGF and BTC are formed by a previously undescribed mechanism that requires co-expression of two distinct receptors. Additional data utilizing MDA MB134 human breast carcinoma cells, which naturally express ErbB2 and ErbB3 in the absence of EGFRs, supported the results obtained employing 32D cells and suggest that EGF and BTC may contribute to the progression of carcinomas that co-express ErbB2 and ErbB3.

Unliganded epidermal growth factor receptor dimerization induced by direct interaction of quinazolines with the ATP binding site

Receptor dimerization is critical for signaling by the epidermal growth factor receptor (EGFR) tyrosine kinase. This occurs after binding of the receptor's extracellular domain by ligand or bivalent antibodies. The role of other receptor domains in dimerization is less clear, and there are no examples of dimers induced by direct perturbation of the EGFR kinase domain. Submicromolar concentrations of AG-1478 and AG-1517, quinazolines specific for inhibition of the EGFR kinase, induced reversible receptor dimerization in vitro and in intact A431 cells. Consistent with the inhibitory effect of quinazolines on receptor kinase activity, the dimers formed lacked a detectable Tyr(P) signal. Quinazoline-induced EGFR dimerization was abrogated in vitro by ATP and the ATP analog adenyl-5'-yl imidodiphosphate. Receptors with a single-point mutation in the ATP binding site as well as wild-type EGFR with a covalent modification of the ATP site failed to dimerize in response to AG-1478 and AG-1517. These data suggest that EGFR dimerization can be induced by the interaction of quinazolines at the ATP site in the absence of receptor ligand binding. In SKBR-3 cells, the quinazolines induced the formation of inactive EGFR/ErbB-2 heterodimers, potentially sequestering ErbB-2 from interacting with other coreceptors of the ErbB family. Structural studies of the quinazoline interaction with the EGFR tyrosine kinase domain should allow for an analysis of receptor-specific chemical features required for binding to the ATP site and disruption of signaling, a strategy that can be perhaps applied to other tumor cell receptor systems.

Bivalence of EGF-like ligands drives the ErbB signaling network

Signaling by epidermal growth factor (EGF)-like ligands is mediated by an interactive network of four ErbB receptor tyrosine kinases, whose mechanism of ligand-induced dimerization is unknown. We contrasted two existing models: a conformation-driven activation of a receptor-intrinsic dimerization site and a ligand bivalence model. Analysis of a Neu differentiation factor (NDF)-induced heterodimer between ErbB-3 and ErbB-2 favors a bivalence model; the ligand simultaneously binds both ErbB-3 and ErbB-2, but, due to low-affinity of the second binding event, ligand bivalence drives dimerization only when the receptors are membrane anchored. Results obtained with a chimera and isoforms of NDF/neuregulin predict that each terminus of the ligand molecule contains a distinct binding site. The C-terminal low-affinity site has broad specificity, but it prefers interaction with ErbB-2, an oncogenic protein acting as a promiscuous low-affinity subunit of the three primary receptors. Thus, ligand bivalence enables signal diversification through selective recruitment of homo- and heterodimers of ErbB receptors, and it may explain oncogenicity of erbB-2/HER2.

The ErbB signaling network in embryogenesis and oncogenesis: signal diversification through combinatorial ligand-receptor interactions

Ligand-induced activation of receptor tyrosine kinases (RTK) results in the initiation of diverse cellular pathways, including proliferation, differentiation and cell migration. The ErbB family of RTKs represents a model for signal diversification through the formation of homo- and heterodimeric receptor complexes. Each dimeric receptor complex will initiate a distinct signaling pathway by recruiting a different set of Src homology 2- (SH2-) containing effector proteins. Further complexity is added due to the existence of an oncogenic receptor that enhances and stabilizes dimerization but has no ligand (ErbB-2), and a receptor that can recruit novel SH-2-containing proteins, but is itself devoid of kinase activity (ErbB-3). The resulting signaling network has important implications for embryonic development and malignant transformation.

ErbB receptors and EGF-like ligands: cell lineage determination and oncogenesis through combinatorial signaling

The ErbB/HER family of transmembrane receptor tyrosine kinases includes four members that bind more than two dozens ligands sharing an epidermal growth factor- (EGF)3 like motif. This family plays a pivotal role in cell lineage determination in a variety of tissues, including mesenchyme-epithelial inductive processes and the interactions between neurons and muscle, glia and Schwann cells. Certain ligands and receptors of the family, especially the ErbB-2 receptor tyrosine kinase, contribute to a relatively virulent phenotype of some human tumors; most notable are carcinomas of secretory epithelia. This large variety of biological signals is generated through a combinatorial network of signal transduction in which different ErbB ligands are apparently capable of stabilizing discrete homo- and heterodimeric receptor complexes, each coupled to a specific set of cytoplasmic signaling proteins. Because each receptor is unique in terms of catalytic activity, cellular routing and transmodulation, the resulting network allows not only an enormous potential for signal diversification but also fine tuning and stringent control of cellular functions. ErbB-2 emerges as a master coordinator of the network, prolonging and amplifying signaling by decelerating the dissociation rates of its heterologous ligands. Thus, the tumorigenic action of ErbB-2 may be attributed to its ability to act as a shared signaling subunit, rather than by functioning as a bone fide receptor.

Trans receptor inhibition of human glioblastoma cells by erbB family ectodomains

Our aim has been to understand the features of erbB receptor homo- and heterodimer assembly to develop approaches to disrupt receptor activation. We have developed a general approach to cause erbB receptor-specific trans inhibition of human neoplasia. The clonal progression of human astrocytomas to a more malignant phenotype often involves the amplification and overexpression of the epidermal growth factor receptor (EGFr) gene. We have selectively targeted the EGFr in human glioblastoma cells with kinase-deficient mutants of the erbB family derived from the ectodomain of the Neu oncogene that are able to form heterodimers with EGFr and inhibit EGFr-dependent phenotypes. In EGFr-positive U87MG human glioblastoma cells, expression of the Neu ectodomain inhibits EGF-, but not platelet-derived growth factor-, induced DNA synthesis; inhibits cell proliferation in the presence of EGF, but not platelet-derived growth factor; inhibits the ability of U87MG to form colonies in soft agar; and inhibits transforming efficiency in athymic mice. These studies establish that EGFr-mediated signal transduction is important in the maintenance of malignant glioma, and that trans receptor inhibition is a novel way to abrogate abnormal growth of these tumors. Neu ectodomains will be useful in determining the manner in which the EGFr contributes to glial tumorigenesis and in the design of pharmaceuticals that disable erbB family oncoproteins. In addition, these studies provide a rationale for the application of the Neu ectodomain in gene therapy approaches to human malignant glioma and, potentially, to other systemic epithelial malignancies expressing erbB family receptors.

Structural aspects of the epidermal growth factor receptor required for transmodulation of erbB-2/neu

The epidermal growth factor receptor (EGF-R) is known to transmodulate the activity and level of the erbB-2/neu protein in several epithelial cell lines. We therefore determined which structural features of the EGF-R were important in transmodulating erbB-2. We found that the addition of EGF to nontransformed epithelial cells resulted in down-regulation of erbB-2 with the same kinetics and similar extent as the EGF-R. By using cells expressing a series of EGF-R modified by site-directed mutagenesis, we found that EGF-R tyrosine kinase activity was not necessary for down-regulation of erbB-2, but receptor sequences between 899 and 958 in the EGF-R were required. To determine whether transmodulation was associated with activation of erbB-2, tyrosine phosphorylation of erbB-2 was determined following addition of EGF. Again, phosphorylation of erbB-2 following EGF addition did not require the intrinsic tyrosine kinase activity of the EGF-R, but did require sequences between 899 and 958. To determine the localization of EGF-R and erbB-2 following EGF addition, the relative distribution of the two receptors was evaluated by fluorescence microscopy. Surprisingly, the majority of erbB-2 was found in small cytoplasmic vesicles, whereas the EGF-R was predominantly found on the cell surface. Addition of EGF resulted in a redistribution and consequent colocalization of both receptors in endosomal and lysosomal structures. We conclude that activation and transmodulation of erbB-2 does not require intrinsic tyrosine kinase activity of the EGF-R, but does require sequences in the EGF-R which regulate its trafficking.

Epidermal growth factor and amphiregulin up-regulate matrix metalloproteinase-9 (MMP-9) in human breast cancer cells

The EGF family of proteins encompasses several polypeptides such as epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha), amphiregulin (AR) and heregulin (HRG-beta 1). These polypeptides regulate proliferation in breast cancer cells through interaction with membrane receptors. It has been previously shown that high EGF receptor number correlates with aggressive behavior and increased metastasis in human breast cancer. In the present study, we investigated the association between EGF and EGF-like ligand-induced DNA synthesis and secretion of MMP-9 and MMP-2 in metastatic SKBR-3 and non-metastatic MCF-7 breast cancer cells. Exposure of SKBR-3 cells to EGF or AR induces expression of MMP-9 but has no effect on MMP-2 secretion. In contrast to EGF and AR, HRG had no effect on gelatinase induction. None of the EGF polypeptides had any effect on gelatinase induction in MCF-7 non-metastatic breast cancer cells. While a relatively specific inhibitor of EGF receptor tyrosine kinase, PD 153035, inhibited EGF-, AR- and HRG-induced cell proliferation, it had no effect on MMP-9 induced by EGF and AR. Experimental evidence suggests that signaling mechanisms for cell proliferation and MMP-9 induction are mediated by different pathways down-stream of EGF receptor autophosphorylation or that low levels of EGF-induced signal that escape inhibition are sufficient to induce MMP-9 but unable to support cell proliferation. In addition, our results suggest that EGF and AR may modulate invasion of metastatic breast cancer cells by increasing the expression of MMPs.

The relationship between human epidermal growth-like factor receptor expression and cellular transformation in NIH3T3 cells

A collection of cell lines expressing each human epidermal growth factor receptor (HER) family member alone or in all pairwise combinations in a clone of NIH3T3 cells (3T3-7d) devoid of detectable epidermal growth factor receptor family members has been generated. Transformation, as measured by growth in soft agar, occurred only in the presence of appropriate ligand and only in cells expressing two different HER family members. Transfection of oncogenic neu (Tneu), conferred ligand-independent transformation only in cells which co-expressed HER1, HER3, or HER4, but not when expressed alone or with HER2. Cell lines were also tested for their ability to form tumors in animals. None of the cell lines expressing single HER family members was able to form tumors in animals with the exception of HER1, which was weakly tumorigenic. Although unable to form tumors when expressed alone, HER2 was tumorigenic when expressed with HER1 or HER3, but not HER4. Of all complexes analyzed, cells expressing HER1 + HER2 were the most aggressive. The relationship between HER1 activation, intracellular calcium fluxes, and phospholipase Cgamma1 activation is well established. We found that activation of HER1 was required for the induction of a calcium flux and the phosphorylation of phospholipase Cgamma1. These activities were independent of, and unaffected by, the co-expression of any other family member. Further, heregulin stimulation of all cell lines including those containing HER1 did not demonstrate any effect on intracellular calcium levels or phospholipase Cgamma1 phosphorylation. This demonstrates that heregulin induced cellular transformation by activating HER3- and HER4-containing complexes does not require the activation of either phospholipase Cgamma1 or the mobilization of intracellular calcium.

A hierarchical network of interreceptor interactions determines signal transduction by Neu differentiation factor/neuregulin and epidermal growth factor

The ErbB family includes four homologous transmembrane tyrosine kinases. Whereas ErbB-1 binds to the epidermal growth factor (EGF), both ErbB-3 and ErbB-4 bind to the Neu differentiation factors (NDFs, or neuregulins), and ErbB-2, the most oncogenic family member, is an orphan receptor whose function is still unknown. Because previous lines of evidence indicated the existence of interreceptor interactions, we used ectopic expression of individual ErbB proteins and their combinations to analyze the details of receptor cross talks. We show that 8 of 10 possible homo-and heterodimeric complexes of ErbB proteins can be hierarchically induced by ligand binding. Although ErbB-2 binds neither ligand, even in a heterodimeric receptor complex, it is the preferred heterodimer partner of the three other members, and it favors interaction with ErbB-3. Selective receptor overexpression in human tumor cells appears to bias the hierarchical relationships. The ordered network is reflected in receptor transphosphorylation, ErbB-2-mediated enhancement of ligand affinities, and remarkable potentiation of mitogenesis by a coexpressed ErbB-2. The observed superior ability of ErbB-2 to form heterodimers, in conjunction with its uniquely high basal tyrosine kinase activity, may explain why ErbB-2 overexpression is associated with poor prognosis.

Synergistic interaction of the Neu proto-oncogene product and transforming growth factor alpha in the mammary epithelium of transgenic mice

Transgenic mice expressing either the neu proto-oncogene or transforming growth factor (TGF-alpha) in the mammary epithelium develop spontaneous focal mammary tumors that occur after a long latency. Since the epidermal growth factor receptor (EGFR) and Neu are capable of forming heterodimers that are responsive to EGFR ligands such as TGF-alpha, we examined whether coexpression of TGF-alpha and Neu in mammary epithelium could cooperate to accelerate the onset of mammary tumors. To test this hypothesis, we interbred separate transgenic strains harboring either a mouse mammary tumor virus/TGF-alpha or a mouse mammary tumor virus/neu transgene to generate bitransgenic mice that coexpress TGF-alpha and neu in the mammary epithelium. Female mice coexpressing TGF-alpha and neu developed multifocal mammary tumors which arose after a significantly shorter latency period than either parental strain alone. The development of these mammary tumors was correlated with the tyrosine phosphorylation of Neu and the recruitment of c-Src to the Neu complex. Immunoprecipitation and immunoblot analyses with EGFR- and Neu-specific antisera, however, failed to detect physical complexes of these two receptors. Taken together, these observations suggest that Neu and TGF-alpha cooperate in mammary tumorigenesis through a mechanism involving Neu and EGFR transactivation.

Targeted inhibition of tumour cell growth by a bispecific single-chain toxin containing an antibody domain and TGF alpha

Overexpression of the epidermal growth factor receptor (EGFR) and ErbB-2 has been observed in a variety of human tumours, making these receptors promising targets for directed tumour therapy. Since many tumour cells express both ErbB-2 and EGFR and these receptors synergise in cellular transformation, therapeutic reagents simultaneously binding to ErbB-2 and EGFR might offer advantages for tumour therapy. We have previously described the potent anti-tumoral activity of a bispecific antibody toxin that contains ErbB-2- and EGFR-specific single-chain Fv (scFv) domains. Here we report the construction and functional characterisation of a novel bispecific recombinant toxin, scFv(FRP5)-TGF alpha-ETA. The fusion protein consists of the antigen-binding domain of the ErbB-2-specific MAb, FRP5, and the natural EGFR ligand, TGF alpha, inserted at different positions in truncated Pseudomonas exotoxin A. ScFv(FRP5)-TGF alpha-ETA protein displayed binding to EGFR and ErbB-2, thereby inducing activation of the receptors, which was dependent on the cellular context and the level of EGFR and ErbB-2 expression. The bispecific molecule was cytotoxic in vitro for tumour cells expressing various levels of the target receptors. In vivo scFv(FRP5)-TGF alpha-ETA potently inhibited the growth of established A431 tumour xenografts in nude mice.

Transformation of NIH 3T3 cells by HER3 or HER4 receptors requires the presence of HER1 or HER2

Members of the epidermal growth factor receptor (EGFR) subfamily of receptor protein tyrosine kinases have been implicated in the pathogenesis of various malignancies. The ability of one EGFR subfamily member to influence, or function synergistically with, another is likely to be a general feature of these receptors. To assess the role of receptor heterodimerization, we analyzed the ability of Neu differentiation factor (NDF) to induce cell growth and transformation of NIH 3T3 cells transfected with different combinations of the EGFR subfamily of receptors. NDF induced mitogenesis, but not transformation, of cells expressing either HER3 or HER4 alone. However, NDF-induced cell transformation was observed when either HER1 or HER2 was coexpressed with HER3 or HER4. In analogous receptor phosphorylation experiments, NDF-induced transphosphorylation appears to be correlated with synergistic transformation of NIH 3T3 cells. Interestingly, transphosphorylation between HER1 and HER4 can be stimulated by either EGF or NDF.

Lack of prognostic significance of epidermal growth factor receptor and the oncoprotein p185HER-2 in patients with systemically untreated non-small-cell lung cancer: an immunohistochemical study on cryosections

The prognostic role of the epidermal growth factor receptor (EGFR) and the related receptor p185HER-2 in lung cancer is as yet undefined. We investigated the immunohistochemical expression of EGFR (monoclonal antibody R1; Amersham) and p185HER-2 (polyclonal antibody A485; Dako) in cryosections. A total of 186 unselected and systemically untreated patients with non-small-cell lung cancer (NSCLC) diagnosed and treated at Odense University Hospital, Denmark, were included. Median follow-up period was 66 months. EGFR and p185HER-2 was highly expressed in 55% and 26% of cases respectively. Expression of EGFR was independent of p185HER-2 expression. The expression of EGFR was higher in squamous cell carcinomas whereas the level of p185HER-2 staining was higher in adenocarcinomas. Expression of either or both receptors was not correlated with age, histological grading, stage and prognosis. We conclude that immunohistochemical detection of these growth factor receptors failed to demonstrate a prognostic significance in patients operated on for NSCLC.

Structural analysis of p185c-neu and epidermal growth factor receptor tyrosine kinases: oligomerization of kinase domains

The epidermal growth factor receptor (EGFR) and p185c-neu proteins associate as dimers to create an efficient signaling assembly. Overexpression of these receptors together enhances their intrinsic kinase activity and concomitantly results in oncogenic cellular transformation. The ectodomain is able to stabilize the dimer, whereas the kinase domain mediates biological activity. Here we analyze potential interactions of the cytoplasmic kinase domains of the EGFR and p185c-neu tyrosine kinases by homology molecular modeling. This analysis indicates that kinase domains can associate as dimers and, based on intermolecular interaction calculations, that heterodimer formation is favored over homodimers. The study also predicts that the self-autophosphorylation sites located within the kinase domains are not likely to interfere with tyrosine kinase activity, but may regulate the selection of substrates, thereby modulating signal transduction. In addition, the models suggest that the kinase domains of EGFR and p185c-neu can undergo higher order aggregation such as the formation of tetramers. Formation of tetrameric complexes may explain some of the experimentally observed features of their ligand affinity and hetero-receptor internalization.

ErbB-2 is a common auxiliary subunit of NDF and EGF receptors: implications for breast cancer

Overexpression of the erbB-2 gene contributes to aggressive behavior of various human adenocarcinomas, including breast cancer, through an unknown molecular mechanism. The erbB-2-encoded protein is a member of the ErbB family of growth factor receptors, but no direct ligand of ErbB-2 has been reported. We show that in various cells ErbB-2 can form heterodimers with both EGF receptor (ErbB-1) and NDF receptors (ErbB-3 and ErbB-4), suggesting that it may affect the action of heterologous ligands without the involvement of a direct ErbB-2 ligand. This possibility was addressed in breast cancer cells through either overexpression of ErbB-2 or by blocking its delivery to the cell surface by means of an endoplasmic reticulum-trapped antibody. We report that ErbB-2 overexpression enhanced binding affinities to both EGF and NDF, through deceleration of ligand dissociation rates. Likewise, removal of ErbB-2 from the cell surface almost completely abolished ligand binding by accelerating dissociation of both growth factors. The kinetic effects resulted in enhancement and prolongation of the stimulation of two major cytoplasmic signaling pathways, namely: MAP kinase (ERK) and c-Jun kinase (SAPK), by either ligand. Our results imply that ErbB-2 is a pan-ErbB subunit of the high affinity heterodimeric receptors for NDF and EGF. Therefore, the oncogenic action of ErbB-2 in human cancers may be due to its ability to potentiate in trans growth factor signaling.

A tyrosine kinase profile of prostate carcinoma

Tyrosine kinases play central roles in the growth and differentiation of normal and tumor cells. In this study, we have analyzed the general tyrosine kinase expression profile of a prostate carcinoma (PCA) xenograft, CWR22. We describe here an improved reverse transcriptase-PCR approach that permits identification of nearly 40 different kinases in a single screening; several of these kinases are newly cloned kinases and some are novel. According to this, there are 11 receptor kinases, 9 nonreceptor kinases, and at least 7 dual kinases expressed in the xenograft tissue. The receptor kinases include erbB2, erbB3, Ret, platelet-derived growth factor receptor, sky, nyk, eph, htk, sek (eph), ddr, and tkt. The nonreceptor kinases are lck, yes, abl, arg, JakI, tyk2, and etk/bmx. Most of the dual kinases are in the mitogen-activating protein (MAP) kinase-kinase (MKK) family, which includes MKK3, MKK4, MEK5, and a novel one. As a complementary approach, we also analyzed by specific reverse transcriptase-PCR primers the expression profile of erbB/epidermal growth factor receptor family receptors in a variety of PCA specimens, cell lines, and benign prostatic hyperplasia. We found that erbB1, -2, and -3 are often coexpressed in prostate tissues, but not in erbB4. The information established here should provide a base line to study the possible growth and oncogenic signals of PCA.

Involvement of ErbB2 in the signaling pathway leading to cell cycle progression from a truncated epidermal growth factor receptor lacking the C-terminal autophosphorylation sites

To investigate the mechanisms underlying the enhanced mitogenic activity of the truncated epidermal growth factor receptor (EGFR) lacking the C-terminal autophosphorylation sites (Delta973-EGFR), we studied the intracellular signaling pathways in NR6 cells expressing human wild type EGFR and Delta973-EGFR. Microinjection of dominant/negative p21ras(N17) completely inhibited EGF-induced DNA synthesis in both cell types. EGF stimulated Shc phosphorylation as well as the formation of wild type EGFR.Shc complexes. In contrast, EGF stimulated Shc phosphorylation without formation of Delta973-EGFR.Shc complexes. Tyrosine-phosphorylated Shc formed complexes with Grb2.Sos, and microinjection of anti-Shc antibody and Shc-SH2 GST fusion protein inhibited EGF stimulation of DNA synthesis in both cell lines. EGF markedly increased ErbB2 tyrosine phosphorylation in wild type EGFR cells. In Delta973-EGFR cells, ErbB2 was tyrosine phosphorylated in the basal state and EGFR stimulated further phosphorylation of ErbB2. In addition to ErbB2, additional proteins were tyrosine phosphorylated in Delta973-EGFR cells, mostly in the molecular mass range of 120 170 kDa. Taken together with our findings indicating coupling of ErbB2 to Shc, these data suggest the importance of an alternative signaling pathway in Delta973-EGFR cells mediated by the formation of heterodimeric structures between the truncated EGFR and ErbB2, followed by coupling through Shc to Grb2.Sos and the p21ras pathway, ultimately leading to mitogenesis.

A bivalent single-chain antibody-toxin specific for ErbB-2 and the EGF receptor

ErbB-2 and EGF receptors are often co-expressed in human tumors and have been shown to synergize in the transformation of cells in experimental model systems. Transactivation of ErbB-2 can occur via ligand-induced heterodimerization with EGF receptor or other members of the ErbB family of receptor tyrosine kinases. We have previously described the potent anti-tumoral activity of the monospecific single-chain antibody-toxins scFv(FRP5)-ETA and scFv(225)-ETA binding to, respectively, ErbB-2 and the EGF receptor. Here we report the construction and functional characterization of a novel bivalent, bispecific single-chain antibody-toxin, scFv2(FRP5/225)-ETA. The fusion protein consists of 2 scFv domains specific for ErbB-2 and the EGF receptor linked to a modified Pseudomonas exotoxin A. ScFv2(FRP5/225)-ETA displayed in vitro cell killing activity on tumor cells overexpressing either ErbB-2 or the EGF receptor similar to that of the monospecific toxins. It was more potent in vitro and in vivo in inhibiting the growth of tumor cells expressing both receptors. Treatment of A431 cells with scFv2(FRP5/225)-ETA led to an increase in EGF receptor and ErbB-2 phosphotyrosine content, most likely via the induction of receptor heterodimers. This may explain the enhanced toxicity of the bispecific antibody-toxin.

Association of signaling proteins with a nonmitogenic heterodimeric complex composed of epidermal growth factor receptor and kinase-inactive p185c-neu

The functional consequences of heterodimer formation between the epidermal growth factor receptor (EGFr) and the p185c-neu receptor tyrosine kinase include increased mitogenic and transformation potencies. To determine the possible alteration of signal transduction pathways resulting from this heteromeric complex, the capacity of several signaling proteins to associate with the heterodimeric receptors has been assayed. The in vivo interaction with the EGFr/p185c-neu heterodimer of several signal transduction proteins, including phospholipase C-gamma 1 (PLC-gamma 1), the p85 subunit of phosphotidylinositol 3-kinase, the ras GTPase activating protein, SHC, NCK, p72RAF, and the tyrosine phosphatase SHPTP2, was measured by coimmunoprecipitation. The binding of these signaling proteins to a complex composed of EGFr and a kinase-inactive form of p185 (p185K757M) was not impaired, even though the mitogenic and transformation activity of this complex had been abrogated. In addition, the EGF-induced phosphorylation of GAP, p85, and PLC-gamma 1 did not correlate with the dominant-negative action of p185K757M on EGFr function. Thus, substrate association and phosphorylation do not correlate stringently with the mitogenic and transforming activity of this receptor complex, suggesting additional pathways or mechanisms vital to EGFr/p185c-neu heterodimeric signaling.

Dual regulation of the epidermal growth factor family of growth factors in breast cancer by sex steroids and protein kinase C

There has been increased interest in the last few years in seeking a better understanding of the local regulation of polypeptide growth factors by systemic hormones, such as sex steroids and by polypeptide hormones. Growth factors and systemic hormones play pivotal roles in hormone-regulated cancers such as breast cancer. In this review, we discuss the regulation of members of the epidermal growth factor (EGF) family by sex steroids and by regulators of the polypeptide hormone signal transduction enzyme termed protein kinase C (PKC). Regulation of the EGF family of genes will be discussed as a model system to evaluate interactions between these two important types of regulatory pathways in breast cancer.

Unexpected transcriptional signals in normal and mitotically defective cells mediated through cytokine and growth factor receptors

Polypeptide growth factors and cytokines mediate their biochemical functions through their responsive receptors. Known cytokine receptors do not possess intrinsic kinase domains whereas several polypeptide growth factor receptors do. Nevertheless, both classes of ligands are capable of activating sets of overlapping genes. In human epidermoid carcinoma cells, for example, both cytokines and epidermal growth factor (EGF) promote a common transcriptional activation signal through the tyrosine phosphorylation of stat91 (signal transducer and activator of transcription) proteins. The stat family of cytoplasmic proteins also appear to have dual functions. Tyrosine phosphorylated 'stats' are employed for signal transduction and, second, for activation of transcription of several genes. The transcription factor-SIE-DNA binding patterns are now known to be different for EGF and interferon-gamma IFN-gamma-treated cells. Nevertheless, in the active DNA-bound complex, the stat91 polypeptide is a component found in either EGF or INF-gamma-treated extracts. Other stat family members of transcription factors may also be present in the complexes. In this case, tyrosine phosphorylated stat91 polypeptides may form into homodimeric or heterodimeric assemblies with other stat-related transcription factors. We describe a novel stat-related factor, p93, that is found in EGF-treated A431 cell extracts but appears to be absent in bovine fibroblast growth factor (bFGF), IFN-gamma, tumor necrosis factor-alpha (TNF-alpha), and untreated cells. p93 appears to be antigenically related to stat91. p185c-neu+, EGFr+ (M1), and p185c-neu- kinase inactive, EGFr+ (NEN757) expressing cells undergo different mitotic responses to EGF. M1 can respond to EGF mitotically while NEN757 cannot. Both cell lines respond to 10 ng/ml of EGF and also to IFN-gamma in transducing transcriptional activation signals to the nucleus, despite the distinct growth response to EGF. Our work has analyzed the stat pathway in these types of cells and found similar patterns of usage despite the distinct EGF-responsive features. Cytoplasmic nonreceptor tyrosine kinases Jak1 and Jak2 may be involved in the activation of stat91 and other transcription factors in EGF and IFN-gamma signaling pathways. Collectively, these studies suggest that the major EGF-stimulated mitotic growth pathways may not be absolutely linked to the stat91 signaling pathways and that such transcription complexes are more complex than previously reported.

Neuregulins and their receptors

The recent identification of an activator for the ErbB2/Neu receptor has uncovered a new family of polypeptide growth factors that undoubtedly play a major role in the regulation of neuronal growth and differentiation. These factors, called the neuregulins, are expressed in neural and mesenchymal tissues, and activate members of the epidermal growth factor family of receptor tyrosine kinases. The identification and characterization of the neuregulins and their receptors will facilitate the dissection of the biochemical pathways regulating nervous system development.

Heregulin activation of extracellular acidification in mammary carcinoma cells is associated with expression of HER2 and HER3

HER2, the erbB-2/neu proto-oncogene product, is a 185-kDa transmembrane glycoprotein related to the epidermal growth factor receptor. Overexpression of HER2 was reported in several human adenocarcinomas, including mammary and ovarian carcinomas. A family of glycoproteins, the heregulin/neu differentiation factors, was characterized and implicated as the ligands for HER2. Recently, it has been shown that HER2 alone is not sufficient to reconstitute high affinity heregulin receptors and that HER3 or HER4 may be the required components of the heregulin receptors on mammary carcinoma cells (Sliwkowski, M.X., Schaefer, G., Akita, R.W., Lofgren, J.A., Fitzpatrick, V.D., Nuijens, A., Fendly, B.M., Cerione, R.A., Vandlen, R.L., and Carraway, K.L., III (1994) J. Biol. Chem. 269, 14661-14665; Plowman, G.D., Green, J.M., Culouscou, J.-M., Carlton, G.W., Rothwell, V.M., and Buckley, W. (1993) Nature 366, 473-475). Using the Cytosensor to measure the extracellular acidification rate, we have examined the effects of recombinant human heregulin-alpha on three mammary carcinoma cell lines expressing HER2 (MDA-MB-453, SK-BR-3, and MCF-7), an ovarian carcinoma cell line expressing HER2 (SK-OV-3), and CHO-K1 and 293-EBNA cells stably transfected with HER2. By reverse transcription polymerase chain reaction and Western blotting, we found that the breast cells also express HER3 and that the ovarian line co-expresses the HER4 message. A dramatic increase in the acidification rate was observed for the mammary carcinoma cells co-expressing high levels of HER2 and HER3. In contrast, the ovarian cells expressing high levels of HER2 and low levels of HER4 or CHO-K1 and 293-EBNA cells expressing HER2 alone were not responsive to heregulin. When these same transfected cells were exposed to monoclonal anti-HER2 antibody followed by anti-IgG to cause aggregation of the HER2 molecules, an increase in the acidification rate was observed, indicating coupling of transfected HER2 to the signal transduction pathway. Transfection of HER2 into MCF-7 cells, on the other hand, gave 4-fold enhanced acidification responses. These data, together with the previously reported high affinity heregulin binding and activation of tyrosine phosphorylation in HER2 and HER3 co-transfected cells support the role of HER2 and HER3 as components of the heregulin receptor in breast cells.

Prevention of breast tumour development in vivo by downregulation of the p185neu receptor

Certain strains of transgenic mice that express the rat neu oncogene (neuT) in mammary epithelial cells develop breast tumours at an average of 44 weeks of age. In this study, intraperitoneal injection of a monoclonal anti-receptor antibody specific for the rat neuT oncogene product dramatically affected tumour development in these transgenic mice in a dose-dependent manner. A significant proportion (50%) of mice, when injected with anti-receptor antibodies, did not develop tumours even after 90 weeks of age. The phosphotyrosine levels of the membrane fraction of breast tissues in the anti-receptor antibody-treated mice were almost completely abolished when a higher dose of antibodies was used. This study demonstrates, for the first time, that immunologic manipulation of an oncogene product can effectively prevent the development of tumours in a rodent transgenic model.

Biological prognostic factors in non-small cell lung cancer

The results of conventional treatments for lung cancer remain poor and long-term survival rates have changed little over the last 10 years. In the same period of time there has been an explosion in the knowledge on the processes of cellular transformation, tumour progression, invasion and metastasis. The major categories of biological events implicated in non-small cell lung cancer include growth factor receptors expression (epidermal growth receptor, p185c-neu), autocrine growth factor production (transforming growth factor alpha), dominant oncogenes activation (ras genes) and deletion of tumour suppressor genes (p53 gene, retinoblastoma gene) and these are some of the abnormalities associated with specific histological types and with poor prognosis. Additional prognostic information can be obtained from the evaluation of the ploidy and proliferative activity of the tumours, carbohydrate antigens expression, presence of neuroendocrine differentiation and the evaluation of markers of the sequential steps involved in the process of tumour dissemination.

The effects of the neuN and neuT genes on differentiation and transformation of mammary epithelial cells

Overexpression of the proto-oncogene product, p185neuN, in a non-tumorigenic mammary epithelial line (31E) facilitates aspects of lactogenic differentiation. Formation of branching cords and induction of beta-casein synthesis by 31E cells normally require co-culture of these cells with fibroblasts, or the presence of collagen or fibronectin. In contrast, 31E cells expressing p185neuN spontaneously form branching cords when grown on tissue culture plastic and can synthesize beta-casein in the absence of exogenous substrates or feeder layers. Under these conditions, the cells deposit laminin and fibronectin, indicating a possible role for p185neuN in the deposition of extracellular matrix proteins. Overexpression of the corresponding oncogene product, p185neuT, has markedly different effects. Expression of p185neuT does not facilitate the formation of branching cords or the synthesis of beta-casein when grown on tissue culture plastic, although these cells do deposit laminin and fibronectin. Confocal microscopy indicates a significant difference in the distribution of laminin and fibronectin in 31E cells expressing p185neuT compared to those expressing p185neuN. The effects of p185neuN and p185neuT expression on cell transformation depend on cell type. Expression of both p185neuN and p185neuT increases anchorage-independent growth of 31E cells, but only p185neuT induces anchorage-independent growth of NIH 3T3 fibroblasts. This lineage specificity in the action of p185neuN may be related to observations that overexpression of p185c-erbB-2 (the human homologue of p185neuN) is only associated with the development of human epithelial cancers. The effects of p185neuN on laminin deposition by 31E cells may be relevant to the transforming ability of p185neuN, since laminin can induce anchorage-independent growth of mouse mammary cells. These results suggest that p185neuN and p185neuT could exert their effects on differentiation and transformation of mammary epithelial cells in part by promoting the deposition of extracellular matrix proteins.

C-erbB-2 immunostaining: problems with interpretation

AIMS

To assess the consistency and reproducibility of assessment of c-erbB-2 immunostaining, and to examine some of the problems relating to inter- and intraobserver variability in the documentation of positive staining; to profile the spectrum of cytoplasmic and membranous staining in a wide range of tumour types.

METHODS

A total of 283 neoplasms were examined for immunohistochemical expression of the c-erbB-2 oncoprotein. Three independent observers were required to assess intensity both of membrane and cytoplasmic staining on a three point and then a four point scale. Extent of positive staining was also assessed on a two point scale. A minimum of two weeks elapsed between assessments using the differing scales.

RESULTS

Positive membrane staining was documented by one or more observers in 16.6% of tumours examined. This positivity was largely restricted to bladder, renal, and breast tumours. The overall level of disagreement as to the presence or absence of membranous staining was 11.3%. Cytoplasmic staining was identified in 55.5% of tumours studied. The level of disagreement as to the presence or absence of cytoplasmic staining was 26.5%.

CONCLUSIONS

Intraobserver variability was minimal, indicating that each pathologist was adhering to internal reproducible standards. Interobserver variability was greater, indicating that the interpretation of c-erbB-2 immunostaining may require set guidelines. It is suggested that assessment should be referenced to a standard positive control, that a three tier system for grading of intensity and a two tier system for grading of extent should be adopted, and that the evaluation should be agreed by at least two pathologists. The presence of cytoplasmic staining should continue to be routinely recorded until its biological role and clinical implications are fully understood.

Infrequent transforming mutations in the transmembrane domain of the neu oncogene in spontaneous rat schwannomas

Ethylnitrosourea (ENU) given transplacentally to rats induces schwannomas of the cranial, spinal, and peripheral nerves, with a high frequency of mutations in the neu proto-oncogene. To establish the requirement for such mutations in tumorigenesis of the Schwann cell, spontaneous schwannomas from BD-VI rats were evaluated for transforming mutations in the transmembrane domain of the protein encoded by the neu proto-oncogene. While all five schwannomas induced transplacentally with ENU were shown to contain T-->A transversions in base 2012 of neu by selective oligonucleotide hybridization and dideoxy sequencing of polymerase chain reaction-amplified products from paraffin sections, only one of nine spontaneous schwannomas from untreated rats had the same mutation. Examination of tumors for mutations in codon 12 of Ki-ras revealed normal alleles. Therefore, the high frequency of mutations in neu in ENU-induced tumors may be directly attributable to the carcinogen or to the period of development at which exposure occurred, and transforming mutations of the transmembrane domain of neu are not required for tumorigenesis of the Schwann cell.

Heterodimerization of epidermal growth factor receptor and wild-type or kinase-deficient Neu: a mechanism of interreceptor kinase activation and transphosphorylation

We have shown that members of the erbB family undergo homodimer and heterodimer formation. The rat p185c-neu and the epidermal growth factor receptor (EGFR) can associate into an active heterodimeric tyrosine kinase. Overexpression of these two receptors also results in a transformed phenotype. We now show that mutant Neu proteins resulting from a point mutation at the ATP-binding site (N757) or cytoplasmic domain deletions (N691stop) are still able to undergo EGF-induced heterodimerization with EGFR. Analysis of heterodimer formation between EGFR and truncated Neu proteins revealed that heterodimerization is preferred over homodimerization of EGFR. N757 can be transphosphorylated by associated EGFR upon EGF stimulation. However, the heterodimer composed of EGFR and N691stop is kinase inactive. These results provided evidence that the Neu ectodomain is sufficient to associate with EGFR physically, and the cytoplasmic domain interaction is required for heterodimeric kinase activation, indicating that Neu/c-erbB2 is not just a simple substrate for EGFR but a transactivator as well.

Demonstration by two-color flow cytometry that tyrosine kinase activity is required for down-modulation of the oncogenic neu receptor

Expression of rat oncogenic neu receptor, p185T-neu (a growth factor receptor with constitutive tyrosine kinase activity), causes cells to become transformed. Treatment with anti-neu receptor monoclonal antibodies reverts the transformed phenotype by down-modulation of p185T-neu. Monoclonal antibody treatment of cells expressing normal neu receptor, p185C-neu (which lacks constitutive tyrosine kinase activity), does not result in down-modulation of p185C-neu. To understand further the role the biochemical activity of p185T-neu plays in transformation and endocytosis, we created a series of mutations in p185T-neu. We found that fibroblasts expressing the tyrosine kinase-defective mutants cannot form foci in culture, colonies in soft agar, or tumors in immunocompromised mice. To follow the antibody-induced endocytosis of neu receptors expressed in these transfectants, we developed a novel two-color flow cytometric assay and confirmed receptor localization by electron microscopy. Cells were treated with mAb7.16.4 over time. After 4 hr of antibody treatment, less than 50% of full-length p185T-neu and of mutant T691 remained on the cell surface, whereas internal expression of the neu receptors within these cells initially increased and then decreased to the original internal receptor level. In contrast, the level of kinase-deficient mutated neu receptors remaining on the cell surface initially decreased by 35%, but, after 4 hr of antibody treatment, the cell surface expression level returned to approximately the original level. Concurrently, fluctuations in expression levels were seen internally over time as well. These cell lines were also treated with gold-conjugated mAb7.16.4. Using electron microscopy, we consistently found the gold particles within multivesicular bodies of cell lines expressing full-length or mutated neu receptor. These data strongly suggest that the fate of the neu receptor, once internalized, is directed by its tyrosine kinase activity. When the kinase activity of the neu receptor is disrupted, the receptor is internalized but recycled to the cell surface, whereas neu receptors which have constitutive kinase activity are internalized and presumably degraded when engaged with anti-neu receptor mAb. Understanding the regulation of receptor endocytosis, degradation, and recycling will contribute to the development of novel therapeutic protocols to combat human malignancies, particularly those associated with the overexpression of the human homologue of the neu receptor, c-erbB2.

What's new in breast cancer? Molecular perspectives of cancer development and the role of the oncogene c-erbB-2 in prognosis and disease

The oncogene c-erbB-2 is frequently amplified in human breast carcinoma. The c-erbB-2 gene is present as a single copy in normal cells, and has been mapped to chromosome 17 in the region 17q 12-21.32. c-erbB-2 encodes a transmembrane glycoprotein known as p185. The intracellular component of p185 has tyrosine kinase activity; the extracellular domain has a structure resembling a growth factor receptor. c-erbB-2 amplification, p185 overexpression and levels of transcribed c-erbB-2 specific messenger RNA have been studied in a large number of breast carcinomas using a variety of techniques. In general, overexpression of p185 oncoprotein reflects various levels of DNA amplification, though in some cases amplification can be detected in the absence of overexpression of p185 and similarly overexpression of p185 can be present without detectable levels of c-erbB-2 amplification. This findings suggests that multiple mechanisms may be responsible for overexpression. c-erbB-2 amplification and/or overexpression occurs in almost all cases of high grade duct carcinoma in-situ, but has been reported in only 10%-40% of infiltrating duct carcinoma. c-erbB-2 amplification or overexpression occurs rarely in invasive lobular carcinoma, and has not been detected in ductal or lobular epithelial hyperplasia, or in atypical ductal or atypical lobular hyperplasia. It is generally believed that c-erbB-2 amplification/overexpression is an important independent prognostic indicator in breast carcinoma, identifying a subset of patients with poor prognosis tumours, particularly if axillary node metasases are present. However, many unanswered questions remain regarding c-erbB-2 and its role in breast cancer development and progression. The causes of c-erbB-2 amplification are unknown. There is no evidence of mutations in the human gene which might cause amplification or overexpression. The significance of the differences in levels of c-erbB-2 amplification/overexpression in in-situ duct carcinoma and associated invasive duct carcinoma has not been established. Amplification or overexpression have not been reported in atypical duct hyperplasia, a proposed precursor of duct carcinoma in-situ, yet overexpression occurs almost always in high grade duct carcinoma in-situ. c-erbB-2 may play a critical role in the development of a clonal in-situ, proliferation of high histological grade, yet does not obviously influence the acquisition of an invasive phenotype. We would postulated that this instability in amplification/overexpression is of biological significance, and if better understood may aid in the study of progression of human breast carcinoma.

Neu and its ligands: from an oncogene to neural factors

Transmembrane receptor tyrosine kinases that bind to peptide factors transmit essential growth and differentiation signals. A growing list of orphan receptors, of which some are oncogenic, holds the promise that many unknown ligands may be discovered by tracking the corresponding surface molecules. The neu gene (also called erbB-2 and HER-2) encodes such a receptor tyrosine kinase whose oncogenic potential is released in the developing rodent nervous system through a point mutation. Amplification and overexpression of neu are thought to contribute to malignancy of certain human adenocarcinomas. The search for soluble factors that interact with the Neu receptor led to the discovery of a 44 kDa glycoprotein that induces phenotypic differentiation of cultured mammary tumor cells to growth-arrested and milk-producing cells. The Neu differentiation factor (NDF or heregulin), however, also acts as a mitogen for epithelial, Schwann and glial cells. Multiple forms of the factor are produced by alternative splicing and their expression is confined predominantly to the central and to the peripheral nervous systems. One identified neuronal function of this family of polypeptides is to control the formation of neuromuscular junctions, but their physiological role in secretory epithelia is still unknown. Other open questions relate to the transmembrane topology of various precursors, the identity of a putative coreceptor, the possible existence of additional ligands of Neu and the functional significance of the interaction between Neu and at least three highly related receptor tyrosine kinases.

Concurrent abnormal expression of ERBB-2, EGFR, and p53 genes and clinical disease progression of breast carcinoma

Metastatic phenotype in human solid tumors is believed to follow stochastic acquisition of structural genetic aberrations-so-called multistep tumor progression. We tested this hypothesis in breast carcinoma by immunostaining 89 stage-heterogeneous cases for the products of three genes (p53, ERBB-2, and EGFR) which are frequently altered in this tumor system. Variable relationships were observed between advanced disease stage and immunostaining for individual gene products (ERBB-2 - p = 0.05, EGFR - p = 0.02, p53 - p = 0.12, Chi Square test). Regional or distant metastases at presentation correlated with multiple oncogene/tumor suppressor gene expression abnormalities: node negative -59% none positive, 29% one positive, 12% two or more positive, vs. node positive -37% none positive, 23% one positive, 39% two or more positive (p = 0.01). Only 2/12 (17%) of tumors with distant metastases at presentation were negative for abnormal expression of any of these gene products, and 7/12 (58%) were positive for two or three. Among axillary node negative patients who developed recurrences, 67% exhibited staining for at least one gene product, compared to only 27% of those without recurrences (p = 0.02). All 5 cases with abnormal staining for each gene product had regional or distant metastases at presentation and recurred. In multivariate analysis, individual expression of p53 outweighed expression of ERBB-2 and EGFR in correlation with outcome. These data suggest clinical neoplastic progression of breast carcinomas correlates with cumulative genetic events detectable by protein expression. Short term recurrence, however, may correlate more closely with abnormal expression of p53 than with EGFR or ERBB-2.

Inverse regulation of human ERBB2 and epidermal growth factor receptors by tumor necrosis factor alpha

Recombinant human tumor necrosis factor (TNF) alpha decreased the expression of ERBB2 mRNA by stimulating p55 TNF receptors of pancreatic tumor cells. This decrease contrasts with an increase in epidermal growth factor receptor (EGFR) mRNA. Both effects were selectively achieved by TNF-alpha or -beta, whereas interferon alpha or gamma or transforming growth factor beta showed no such effects. The inverse regulatory effects of TNF on ERBB2 and EGFR mRNA levels were evoked by different signaling pathways of p55 TNF receptors. The TNF-mediated ERBB2 mRNA decrease was followed by a reduction in protein. Four of five pancreatic tumor cell lines exhibited this down-regulation. This decrease of ERBB2 is a singular example of a modulation of this growth factor receptor by TNF. Overexpression of ERBB2 has been reported to cause resistance to TNF and other cytotoxic cytokines. In our study we show that the TNF-mediated down-regulation of ERBB2 in pancreatic tumor cells is accompanied by an increase in growth inhibition at low doses of TNF. The simultaneous alteration of the ERBB2/EGFR balance by TNF represents a striking model of cytokine receptor transregulation in the growth control of malignant pancreatic epithelial cells.

Overexpression of HER2/neu oncogene in human pancreatic carcinoma

The HER2/neu oncogene encodes a transmembrane protein that possesses intrinsic tyrosine kinase activity. Its overexpression has been associated with the malignant phenotype. In this study we examined HER2/neu expression in the normal and cancerous human pancreas. In the normal pancreas HER2/neu immunostaining was observed in acinar and ductal cells. HER2/neu immunoreactivity was expressed in 34 of 76 (45%) pancreatic carcinomas. There was a significant correlation between tumors with well-differentiated histology and HER2/neu expression. Northern blot analysis demonstrated HER2/neu mRNA expression in the normal pancreas and in situ hybridization confirmed its distribution in both acinar and ductal cells. In cancer tissues Northern blot analysis indicated that HER2/neu mRNA levels were elevated in 13 of 25 (52%) of the tumors in comparison with the normal tissues. In addition, in situ hybridization demonstrated a strong but heterogenous distribution of mRNA grains in these tumors. Southern blot analysis did not demonstrate HER2/neu gene amplification in any of the tumors. These data indicate that the HER2/neu protein is synthesized in the normal exocrine pancreas and is frequently overexpressed in well-differentiated adenocarcinomas of the pancreas as a result of increased HER2/neu mRNA levels.

Interaction of the neu/p185 and EGF receptor tyrosine kinases: implications for cellular transformation and tumor therapy

Growth factor receptors such as the epidermal growth factor receptor (EGFR) and the p185c-neu protein serve vital roles in the transduction of differentiation, developmental, or mitogenic signaling within normal cells. Two methods of analysis suggest that the inappropriately high expression of either protein tyrosine kinase promotes malignant transformation. First, data from in vitro experiments indicate that overexpression of either EGFR or p185c-neu (or the human homolog c-erbB-2) transforms cell-lines. Second, analysis of primary tumors and tumor cell-lines derived from many epithelial tissues (breast, stomach, ovary, and pancreas) show growth factor receptor gene amplification and elevated protein levels. The physical and functional interaction of p185c-neu and EGFR leads to the formation of a highly active, heterodimeric tyrosine kinase complex which synergistically activates cellular transformation. Anti-receptor antibodies have shown potential utility for the down modulation of these cell-surface proteins and suppression of the malignant phenotype. Design of organic antibody "mimetics" based on the structure of antireceptor antibodies may provide useful therapies and biological reagents to affect growth factor receptor function.

Receptor tyrosine kinase expression in astrocytic lesions: similar features in gliosis and glioma

The purpose of this study was to determine if the expression of receptor tyrosine kinases would distinguish astrocytosis from astrocytoma. Because the expression of this family of receptor proteins is greater in higher-grade tumors, a graded series of both reactive and neoplastic astrocytic lesions in humans was evaluated. The reactive processes included both mild gliosis and severe (intense) gliosis. The two immunocytochemically detected membrane receptor proteins, p145 and p185, are those encoded by the kit and neu genes, respectively. Semi-quantitative assessments were made independently for the frequency and intensity of astrocytic immunostaining together with corollary immunocytochemical staining to detect glial fibrillary acidic protein. It was found that both mild gliosis and low-grade astrocytomas only minimally express these receptors. In contrast, severe gliosis and high-grade neoplasms consistently express these receptors at much higher levels. In both astrocytosis and astrocytomas, a cell with abundant perikaryal cytoplasm is most likely to be immunoreactive, often with dense reaction product concentrated at the periphery of the somal cytoplasm. The extent and pattern of immunoreactivity in high-grade astrocytomas preclude the interpretation that all immunoreactive cells were merely reactive astrocytes. We conclude that the expression of these receptors per se does not differentiate astrocytic neoplasia from reactive astrocytosis. Second, we conclude that immunocytochemically detectable levels of neu or kit receptor expression is not constitutive in normal astrocytes and in some stages of astrocytic neoplasia. On the basis of these findings, we speculate that some neoplastic astrocytes maintain and manifest the capacity to respond to transitory exogenous stimuli, as do reactive astrocytes. This reaction could include the elaboration of receptor tyrosine kinases. Alternatively, even if the function of these receptors in gliosis differs from that in gliomas, the common expression could still reflect an "active" state shared by astrocytes in these two processes.

Expression of growth factors and their receptors in human esophageal carcinomas: regulation of expression by epidermal growth factor and transforming growth factor alpha

The expression of mRNAs for epidermal growth factor (EGF), transforming growth factor alpha(TGF alpha), EGFR, platelet-derived growth factor (PDGF) A and B chain, PDGF receptor (PDGFR), transforming growth factor beta (TGF beta), erbB-2 and estrogen receptor (ER) genes was first examined in 6 human esophageal carcinoma cell lines, 6 xenoplanted and 15 surgically resected esophageal carcinomas. Secondly, the effect of EGF and TGF alpha on the expression of these genes by the TE-1 esophageal carcinoma cell line was investigated. The expression of EGF mRNA was detected in 8 (29.6%) of 27 tumors including the cell lines, whereas the TGF alpha and EGFR genes were expressed in 21 (77.8%) and 24 (88.9%) tumors respectively. PDGF B chain and PDGFR were detected in 18 (66.7%) and 20 (74.1%), respectively, and ER mRNA was observed in 16 (59.3%) tumors. Genes for PDGF A chain and TGF beta and the erbB-2 gene were commonly expressed. On the other hand, exogenous EGF and TGF alpha stimulated the expressions of fos and myc genes by TE-1 cells. The expression of mRNAs for TGF alpha, PDGF A and B chain and the erbB-2 genes was also increased after treatment with EGF. TGF alpha increased the accumulation of mRNAs for EGF, TGF alpha, EGFR, PDGF A and B chain and the erbB-2 gene. Moreover, the expression of mRNAs for interstitial collagenase, stromelysin and type IV collagenase was increased after EGF or TGF alpha treatment. These results indicate that EGF and TGF alpha may regulate the multi-growth-factor receptor expression and may play a central role for tumor invasion and metastasis as autocrine modulators for human esophageal carcinoma.